Wet material must be dried to some extent prior to combustion. In an incinerator, such as a rotary kiln, waste is passed through the length of the incinerator while undergoing incineration. If the waste contains a significant amount of water a burden is placed on the combustion process. This is because the wet waste first passes through a heat sink area of the incinerator wherein heat passes into the waste to dry it. Thereafter the dried waste is combusted releasing heat. Unfortunately this heat is downstream of the heat sink area. Accordingly heat must be provided to the heat sink area from a burner. This is disadvantageous not only due to the added capital and operating costs of this burner, but also more importantly because this mode of operation increases the potential for hot spots within the incinerator. Unless the incinerator temperature profile is very closely watched and maintained, there may be hot spots from overheating in the drying or heat sink area, and hot spots in the downstream area where the waste is combusted liberating heat. Maintenance of a proper temperature profile is difficult within an incinerator because the waste generally has a very highly variable water content and heating value. Hot spots, which may occur due to sudden changes in the heat demand within the heat sink area or the heat liberated from the combusting waste, are undesirable because they cause equipment damage or slag buildup and also because they kinetically favor the formation of nitrogen oxides which are considered deleterious pollutants.
In order to avoid these problems, wet waste is sometimes passed through a separate dryer prior to being passed through an incinerator. This complicates and adds to the capital costs of an incineration operation.
Accordingly, it is an object of this invention to provide a method for combusting wet waste wherein the waste is dried within the incinerator without increasing the potential for hot spots within the combustion zone.